WARNING: This page is about a different car, the 2011 BMW 750xi, 2011 BMW 750Lxi, 2010 BMW 750xi, and 2010 BMW 750Lxi. However, it is still accessible from the selected car via links, so may be relevant.
The following illustration shows the arrangement of the power steering components and lines.
Fig 1: Identifying Power Steering Components And Line Arrangement
Courtesy of BMW OF NORTH AMERICA, INC.
Check all visible connections, hoses, lines and steering gear for traces of fluid.